Culturing Tissue-Engineered Constructs of Clinically Relevant Size Using Perfusion

What is in-vitro tissue engineering?

In vitro tissue engineering is a relatively recent phenomenon that usually refers to cell culture systems combining biomaterials, tissue specific cells, and chemicals such as growth factors and cytokines that aim to direct the behaviour of the cells in the way they interact with their material scaffolds, and each other. These tissue engineered constructs may then be used in a variety of model systems, or they may be cultured with the aim of creating a suitable transplant.

Why is it useful?

The advantages of a tissue engineered transplant graft are numerous; patient tailored design, lack of donor site morbidity and the opportunity to use autologous cells in order to avoid the host immune response, to name just a few. The advantages of tissue engineered model systems are similarly numerous, with the most significant probably being the reduction in the research community’s reliance on animal models and improved safety when animal trials are used.

What tissue engineering based problem are Don Whitley Scientific focusing on?

A significant problem usually encountered when engineering porous constructs of larger, more clinically relevant sizes, is that of sufficiently nourishing the whole depth of the scaffold. The thicker a porous construct is, the more difficult it is for nutrients to diffuse into the middle of the construct, and for waste to diffuse out. The result of this in static culture systems is that whilst healthy, well-nourished growth is seen on the external section of the construct, the inner confines become starved and necrotic. The result of this is a compromise in selection of material pore size that balances a pore size large enough to allow spontaneous nutrient exchange, yet small enough to provide the cultured cells with a physiologically relevant environment.

How do our products solve this problem?

Mechanical loading has long been used in the culture and testing of load bearing tissues as it has been identified as an important modulator of tissue physiology, and the TC-3 mechanical stimulation bioreactor is now able to create simultaneous loading and perfusion conditions. This means that it is able to culture porous constructs of clinically relevant size under physiologically relevant compressive forces, whilst at the same time perfusing media through the bottom and into the centre of the construct using a flow system. From the centre of the construct the media is then forced outwards through the exterior of the construct and into the culture chamber where it rests before being removed through the chamber’s outlet, ensuring the whole construct is adequately nourished. This set-up is particularly relevant to bone and cartilage tissue engineering.

Not only does this set-up have the immediate effect of optimising nutrient distribution within the construct, but it also allows researchers to use endothelial cells (for example) and molecules such as Vascular Endothelial Growth Factor to direct the growth of vasculature within the construct to further improve its viability in the event of transplant.

What if the user doesn’t want to use mechanical forces?

In the case of users not culturing tissues with relevant mechanical forces, P3D chambers are plastic culture chambers available in variable diameters and with adjustable length. These culture chambers are designed to house porous scaffolds and be connected to flow circuits in a manner that drives media through the centre of the construct, ensuring even culture throughout. It is possible to culture the cells free of shear stresses at low flow velocities, and it is possible to apply shear stress at high flow velocities. Don Whitley Scientific also supplies a number of pumping solutions for flow systems, from simple peristaltic pumps, to the TEB Series which consist of incubators with built in peristaltic pumps and a software interface that allows programming of complex flow profiles, and also comes with an automated cell seeding programme to ensure a homogeneous, reliable, repeatable seed.

 

Article by Daniel Secker